The present invention relates generally to agricultural implements, and more specifically, to a hydraulic circuit utilized with an integrally mounted implement which permits the normally disabled rockshaft control lever on the tractor to be used to raise the tractor hitch without affecting the rest of the lift assist circuit.
On wide agricultural implements such as row crop cultivators or rotary hoes, the implement tool bar or main frame is connected to the tractor by a three-point hitch. When the tractor hitch is raised to move the implement to the transport position, the entire weight of the implement is transferred to the rear of the tractor which results in partial or complete loss of steering control. To avoid this problem, many large integral implements are fitted with a hydraulically actuated lift assist wheel to reduce the weight transferred to the tractor during transport. Such a system is shown, for example in U.S. Pat. No. 4,193,458 and on commercially available implements such as the John Deere Model 845 Series folding row-crop cultivator. With implements such as the 845 Series row-crop cultivator, implement weight is carried by implement frame gauge wheels when the implement is in the field-working position Such an arrangement limits tractor traction If the operator attempts to raise the tractor hitch to try to transfer some of the load to the rear of the tractor, the tractor center link of the three-point hitch goes slack and the lift assist wheel lowers. Operation of the implement under such conditions is undesirable since the slack center link fails to hold the implement parallel to the ground and the lowered lift assist wheel leaves a track in the field which is unacceptable to the farmer. The rockshaft control lever is essentially useless while the implement is in the field-working position.
In other types of hydraulic circuits for implements with lift assist wheels, such as explained in U.S. Pat. No. 4,193,458 with respect to the John Deere Model 7100 mounted Max-Emerge planter, the operator must synchronize two separate control levers to elevate the implement lift assist wheel and the tractor three-point hitch for transport of the implement. With such a structure, damage to the hitch and implement can result if the cylinders are not operated in near synchronization. Also, such an arrangement requiring simultaneous movement of two levers is more difficult for the farmer to operate.